Silicone pressure-sensitive adhesives (hereinafter also referred to as PSAs) typically contain at least two primary components, namely a linear siloxane polymer and a tackifier resin consisting essentially of triorganosiloxane (M) units (i.e., R.sub.3 SiO.sub.1/2 units, in which R denotes a monovalent organic group) and silicate (Q) units (i.e., SiO.sub.4/2 units). In addition to the above two ingredients, silicone PSA compositions are generally provided with some crosslinking means in order to optimize various properties of the final adhesive product. In view of the high viscosity imparted by the polymer component, these PSA compositions are typically dispersed in an organic solvent for ease of application.
For example U.S. Pat. No. 3,929,704 to Horning teaches a silicone PSA comprising an MQ resin, silicone gum and a curing agent, wherein the curing agent is a peroxide admixed with a plasticizer and an extender. Alternatively, when the silicone polymer contains unsaturated groups in its molecule such silicone PSA compositions can be cured by incorporating an organohydrogenpolysiloxane and a hydrosilation catalyst. European Patent Application No. 355 991 to Minnesota Mining and Manufacturing Company is illustrative of such compositions. In this case, the polymer component comprises a diorganoalkenylsiloxy endblocked polydiorganosiloxane and a diorganohydrogensiloxy endblocked polydiorganosiloxane which allows the formation of a relatively low viscosity PSA composition without the need for a solvent.
The use of certain SiH-functional compounds in conjunction with non-silicone PSAs is also known. Japanese Patent Application No. Hei 4(1992)-145188 to Kanefuchi Chemical Industry Co., Ltd. discloses organic PSAs which are a blend of (A) an alkenyl group containing organic compound or organic polymer, (B) an organic compound containing at least two SiH groups in its molecule, (C) a hydrosilylating catalyst and (D) an organic adhesive resin.
Additionally, Blizzard et al., in U.S. Pat. No. 4,831,080, have demonstrated a method for improving the bond strength of a pressure-sensitive adhesive by contacting two PSA components to form a PSA construction. In this contribution to the art, the first component comprises a conventional PSA and a liquid organohydrogenpolysiloxane and the second component comprises the same PSA and a cure agent for the liquid organohydrogenpolysiloxane. A similar two-component PSA system is described in U.S. Pat. No. 5,037,886, also to Blizzard et al. In this case, the organohydrogenpolysiloxane is reacted with a siloxane resin before being incorporated into the first PSA component and a cure agent for this reaction product is mixed with the second component.
Although silicone PSAs of the prior art including some of the above described systems, do offer the industry considerable advantage over organic counterparts, there still remains room for improvement. Thus, for example, in a silicone pressure-sensitive tape which comprises a silicone PSA layer coated onto a plastic film (e.g., a self-wound tape), it is highly desirable to achieve the simultaneous properties of high adhesion, high tack and smooth adhesive release from substrates at high rates of peel. The latter characteristic is difficult to achieve with some silicone PSAs and an annoying noise, referred to as "chatter" herein, is noted when such a pressure-sensitive tape is unwound from a roll at relatively high speed. Aside from presenting a nuisance in numerous industrial operations, this "chatter" is associated with the unwanted transfer of adhesive from such a tape to the substrate contacted therewith (e.g., the back side of the tape in the previous example) during a rapid peel operation. Furthermore, the uneven adhesive release can be detrimental to process machinery since it can induce vibrations therein especially when a wide roll of tape (e.g., one to two meters) is being unwound.